This invention relates to a food package for controlled heating or cooking of food in hot air, convection, household and microwave ovens.
The rapid increase of microwave oven sales to private households and the development of catering have changed the conditions for the prepared food manufacturers, implying great advantages as well as problems. The advantages are evident and connected with the rapid heating in microwaves which makes frozen prepared food even more convenient. There are two main problems:
The traditional metallic tray is opaque to microwave radiation and is not suitable in microwave ovens, as arcing may occur inside the oven cavity resulting in a very bad perception of this package by the consumer. Since metals are not transparent to microwaves and heating is obtained only from the top, when compared to heating in a plastic container, cooking is not only longer but also uneven, especially with frozen products in which the bottom layer is still frozen while the top layer is overcooked and unacceptable (dry or burnt). PA1 Plastic trays are transparent to microwave radiation but owing to the limited penetration of microwaves and to the different absorptions of microwaves by the components of the products, e.g., water and ice, the cooking of frozen products is uneven. Hot spots appear in the corners and along the walls of the tray while the center is still frozen. PA1 a) the use of a standard cardboard/aluminum laminate, and PA1 b) the use of existing machinery to deposit the shield onto the tray. Such machinery is currently used to produce packages for margarine and butter.
Development work in the package industry in relation to microwave cooking has dealt with the problem of selective cooking of multi-component meals in which the individual food components generally require different quantities of microwave energy exposure.
For example, U.S. Pat. No. 3,865,301 describes a shielded container for a plurality of ingredients of a sandwich-type food product that are to be heated or cooked to a different extent and which is opaque to microwave radiation except for radiation-transparent windows.
U.S. Pat. No. 4,081,646 illustrates a tray of a material transparent to microwave energy with a plurality of compartments, a cover formed of a material that is transparent to microwave radiation and adapted to the tray and a shielding box having walls opaque to microwave energy and bearing apertures at predetermined locations for inserting the tray with the cover therein, in order to control the amount of radiation received by each of the individual components of a meal.
In the prior developments, very little attention has been paid to uneven cooking of a prepared dish within a single compartment or tray in a microwave oven. In U.S. Pat. No. 4,351,997, there is described a new design for a dual ovenable tray to avoid this uneven cooking in microwave ovens. This design is related to a tray including a bottom wall and a peripheral wall ending with a horizontally extending rim. The rim is coated partly or totally with a material reflecting or opaque to microwave radiation, such as an aluminum foil. This provides a package in a tray form which gives an excellent temperature distribution in microwave ovens, and it is possible to use the package in hot air, convection and household ovens at temperatures up to 250.degree. C.
The present invention relates to technical and economical new solutions to achieve such a package.